Head suspension assemblies (HSAs) include, as component elements, a base plate, a load beam, a gimbal flexure and a head assembly. The load beam is an elongated metal spring structure. The base plate is attached to a proximal end of the load beam, and can be configured for mounting the load beam to an actuator arm of a disk drive. The gimbal flexure is positioned on a distal end of the load beam. Mounted to the gimbal flexure is a head assembly, which is thereby supported in read/write orientation with respect to an associated disk. The head assembly comprises a read/write transducer attached to an air bearing structure called a slider.
HSAs suspend the "flying" head assembly nanometers away from the surface of a rotatable data storage device (a spinning disk). The gimbal flexure provides gimballing support, that is, the gimbal flexure positions and maintains the head assembly at a desired flying attitude, a predetermined angle and height in relationship to the disk surface. The static attitude of the head assembly, the position of the head assembly at rest, is calibrated so that when the disk drive is in operation, and the slider is affected by the lifting force of the air stream caused by the rotation of the disk, the head assembly reaches an optimal dynamic attitude (position of the head assembly during operation).
To counter the air lift pressure exerted on the slider during disk drive operation, a predetermined load (a "gram load") is applied through a load point feature on the suspension assembly to a precise load point on the slider. The head flies above the disk at a height established by the equilibrium of the gram load on the load point and the lift force of the air stream. Load point positioning is critical to maintain the head at the desired flying angle. Also, since in a circular disk the outside surfaces have a greater surface speed than the inside surfaces, load point positioning compensates for the air speed differentials between the inside and outside edges of the slider.
A conventional gimbal flexure, sometimes referred to as a Watrous gimballing flexure design, is formed from a single sheet of material and includes a pair of outer flexible arms about a central aperture and a cross piece extending across and connecting the arms at a distal end of the flexure. A flexure tongue is joined to the cross piece and extends from the cross piece into the aperture. A free end of the tongue is centrally located between the flexible arms. The head assembly is mounted to the free end of the flexure tongue.
During attachment of the slider to the flexure tongue, the mounting surface datum (to which the load beam is mounted during HSA assembly) and the slider air bearing surface datum must be at a predetermined orientation with respect to each other (desired relationship). The mounting surface datum and the slider air bearing surface datum are level surfaces used as reference points or surfaces in establishing the desired relationship of the actuator mounting surface and the slider air bearing surface relative to each other (nominal angle). The upper and lower surfaces of the slider are manufactured according to specifications requiring them to be essentially or nominally parallel to each other.
During the process of manufacturing and assembling the HSA, any deviations caused by lack of precision in forming or assembling the individual elements contributes to a lack of planarity in the surfaces of the elements. A buildup of deviations from tolerance limits in the individual elements causes deviation from the desired relationship. The parameters of static roll and static pitch torque in the HSA result from these inherent manufacturing and assembly tolerance buildups. The load point feature of common gimbals does not compensate or help correct these tolerance deviations.
Static roll torque and static pitch torque have their rotational axes at about the center of the slider in perpendicular planar directions, and are caused by unequal forces acting to maintain the desired relationship on the slider while the head assembly is flying over the disk. That is, static torque is defined as a torque or a moment of force tending to cause rotation to a desired static (i.e., reference) attitude about a specific axis.
As applied to a HSA, the longitudinal axis of the slider is parallel and ussually coincident with the longitudinal axis of the load beam and of the HSA. The axis of roll torque is coincident with the longitudinal axis of the HSA. The value of static roll torque is measured on either surface of the static roll torque axis when the flexure tongue is parallel with the base plate. If the flexure has been twisted about the static roll torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along the roll torque axis), the values measured on either surface of the roll torque axis will not be the same. Thus, when the attached slider is in flying attitude to the associated disk surface, force (referred to as an induced roll torque value) is needed to twist the tongue back into desired relationship alignment to the disk.
The axis of pitch torque is perpendicular to the longitudinal axis of the HSA. The value of static pitch torque is measured on either surface of the static pitch torque axis when the flexure tongue is parallel with the base plate. If the flexure has been twisted about the static pitch torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along the pitch torque axis), the values measured on either surface of the pitch torque axis will not be the same. Thus, when the attached slider is in flying attitude to the associated disk surface, force (referred to as an induced pitch torque value) is needed to twist the tongue back into parallel alignment to the disk. It will of course be understood that in actual static and dynamic attitude conditions the flexure can be twisted with respect to both axes, requiring alignment about both the pitch axis and the roll axis.
These torques can also be referred to in terms of static attitude at the flexure/slider interface and in terms of the pitch and roll stiffness of the flexure. The ideal or desired pitch and roll torques are best defined as those which would exist if the components were installed in an ideal desired relationship configuration in a disk drive. In an actual disk drive, pitch and roll static torques produce adverse forces between the air bearing surface of the slider and the disk, affecting the flying height of the slider above the disk, resulting in deviations from optimum read/write transducer and head assembly/disk interface separation.
In the static attitude of a conventional flexure design, the flexure tongue is offset from the flexure toward the slider to allow gimballing clearance between the upper surface of the slider and the lower surface of the flexure. The offset is formed where the flexure tongue and cross piece join, in conjunction with the dimple that is formed on the flexure tongue. The standard flexure design evidences a low value of pitch stiffness and a moderate value of roll stiffness. Pitch stiffness and roll stiffness are each measured in (force.times.distance)/degree.
Thus, gimbal flexure designers desire to achieve a precise method of fabrication that accurately compensates and corrects for manufacturing variations that currently contribute to static pitch and roll torque errors. The manufacturing process should be efficient to perform corrections for static roll torque, as well as for static pitch torque, since the ability to correct for both static torques is needed for proper flexure/slider alignment. Ideally, the manufacturing process should also result in accurate and simple placement of the load point feature.
Formation of pressure-formed surface features, such as dimples or depressions, present accuracy difficulties. To increase manufacturing efficiency and ease of assembly, the number of additional components in a flexure, especially small, delicate components, is preferably reduced. Features and additional components should be cost-efficient, yet able to meet performance requirements. Only precise location of a load point feature allows precise location of the slider flying surface; as the load point shifts from nominal the slider has a tendency to not fly in the proper orientation relative to the disk due to the torque resulting from the off-center load force. Thus, the manufacturing process of the ideal gimbal flexure should use very accurate manufacturing techniques, be cost-effective, and reduce the number of unnecessary manufacturing steps and elements.